多电荷态混合束传输的理论及实验研究

本文对ECR离子源引出的混合束流传输特性进行了较为深入讨论，并在此基础上，对ECR混合束流传输的模拟计算以及空间电荷中和方法，从理论和实验两方面做了较为深入的研究。在同时考虑到离子空间电荷效应，离子一离子碰撞所造成的离子间动量交换，以及离子与管道剩余气体作用、不同电荷态离子之间的作用所造成的电荷交换效应的基础上，结合原子物理方法和蒙特卡罗方法，充分利用计算机可视化程序设计方法，独立成功研制了一套专门的混合束传输程序McIBs1.0，并且对中国科学院近代物理研究所原子试验平台（14.5GHzECR离子源及相关的传输线）做了初步的模拟计算。通过计算发现Glaser透镜确实对离子具有很强的分选作用。同时发现，在一定的条件下，可以依靠Glaser透镜对混合束聚焦形成空心束流。另一方面，对Glaser透镜在ECR混合束传输过程中的作用做了较为深入细致的分析研究。除发现Glaser透镜具有以上所提到的分选功能以及可以在一定条件下形成空心束的功能外，还提出了Glaser透镜和ECR离子源弓！出线包可能能够共同形成磁约束空间电荷透镜的新观点。完成了负高压电极法中和束流空间电荷效应的实验研究，其典型结果是，在负偏压电极加一6KV负高压时，对于O6+，在终端法拉第筒上取得了束流强度与原束流强度相比增加幅度为26％＜△I＜30％的较好试验结果。同时自行构建模型，对其做了仔细的理论分析和计算。针对 ECR高电荷态强流离子束，在该领域首次独立提出使用负电性气体中和高电荷态混合离子束空间电荷效应的新方法，完成实验，证明了其可行性和可靠性。并取得了通过该方法，使O7+束流稳定增加12％、Ar11+束流稳定增长14％、Ar8+稳定增长39％的较好结果。

CSRm内靶实验中的轻离子束流储存寿命研究

束流储存寿命对于储存环的建造和内靶实验都是一个很重要的参数。由于重离子冷却储存环工程的优化，HIRFL-CSR主环将能提供2．SGev的质子束流，这为强子物理研究提供了一个很好的平台。设计并建立一套针对强子物理的内靶系统己经列入到计划当中，与内靶相关的束流储存寿命研究也随之展开。本论文首先分析了在内靶实验中束流储存寿命的影响因素，即真空管道中的残余气体分子、冷却电子束和内靶，以及束内散射和集体效应等，并用理论解析和数值计算的方法，对各种因素的影响程度进行估算。研究表明，内靶散射影响下的束流储存寿命比其他因素导致的短2～3个数量级，内靶是影响束流寿命的决定性因素。其次，对CSRm将来实验中主要用到的Pelle七内靶和碳薄膜靶做了简要介绍，并计算了它们的有效靶厚大约为lx10、切ms／cmZ和5火1017atoms／CmZ。再者，用理论推导方法，对内靶的多次库仑散射和束流能量损失扰动对束流的影响进行了研究，推导了束流的横向和纵向发射度增长与束流每次打靶产生的小库仑散射角均方值气s和相对动量分散气了：之间的关系，并通过数值计算的方法给出了CSRm内靶实验条件的发射度增长曲线。最后，建立了内靶散射的MOnte-Carlo模拟程序，在模拟数据的基础上，总结研究束流的发射度增长规律，以及束流存储寿命与内靶厚度和束流能量的关系。计算表明，当存在Pellet靶（1、1016atoms／cm2）和c膜（5*1017 atoms／cmZ）时，2800Mev质子束的束流储存寿命分别为397秒和0．7秒，将来的内靶实验亮度大约为2 x 1033cm-2·s-1。

HIRFL剥离器后切束线物理设计

HIRFL is a tandem cyclotron complex for heavy ion. On the beam line between SFC and SSC, there is a stripper. Behind it, the distribution of charge states of beam is a Gauss distribution. The equilibrium charge state Q_0 is selected by 1BO2(a 50° dipole behind the stripper) and delivered to SSC. One of two new small beam line (named SLAS) after 1B02 will be builded in or der to split and deliver the unused ions of charge states (Q_0 ± n) to aspecific experimental area. Q_0 ± n ions are septumed and separated from initial(Q_0) ion beam by two septum magnets SM1, SM2. The charge state selected by SM1 will be Q_0 ± 1(6 ≤ Q_0 < 17), Q_0 ± 2(17 ≤ Q_0 < 33) and Q_0 ± 3 (Q_0 ≥ 33) forming a beam in one of the two possine new beam line with the stripping energy of (0.2 to 9.83 Mev/A), an emittance of 10π mm.mrad in the two transverse planes and an intensity ranging from 10~(11) pps for z ≤ 10 to some 10~5 pps for the heaviest element. Behind SM2, a few transport elements (three dipoles and seven qudrupoles) tra nsport Q_0 ± n beam to target positions T1, T2 (see fig. 1) and generate small beam spots (φ ≤ 4mm, φ ≤ 6mm). The optics design of the beam line has been done based on SLAC-75 (a first and second - order matrix theory). beam optics calculation has been worked out with the TRANSPORT program. The design is a very economical thinking, because without building a new accelerator we can obtain a lower energy heavy ion beam to provide for a lot of atomic and solid state physical experiments

Electrical conductivity of a single Au/polyaniline microfiber

We report the measurements of conductivity, I-V curve, and magnetoresistance of a single Au/polyaniline microfiber with a core-shell structure, on which a pair of platinum microleads was attached by focused ion beam. The Au/polyaniline microfiber shows a much higher conductivity (similar to 110 S/cm at 300 K) and a much weaker temperature dependence of resistance [R(4 K)/R(300 K)=5.1] as compared with those of a single polyaniline microtube [sigma(RT)=30-40 S/cm and R(4 K)/R(300 K)=16.2]. The power-law dependence of R(T)proportional to T-beta, with beta=0.38, indicates that the measured Au/polyaniline microfiber is lying in the critical regime of the metal-insulator transition. In addition, the microfiber shows a H-2 dependent positive magnetoresistance at 2, 4, and 6 K.

Surface roughness characterization of soft x-ray multilayer films on the nanometer scale

The soft x-ray reflectivity of multilayer films is affected by the surface roughness on the transverse nanometer scale. Scanning tunneling microscopy (STM) is an ideal instrument for providing high-lateral-resolution roughness measurements for soft x-ray multilayer films that cannot be obtained with other types of instruments on the transverse nanometer scale. The surface roughnesses of Mo/Si, Mo/C, and W/Si soft x-ray multilayer films prepared by an ion-beam-sputtering technique were measured with a STM on the vertical and transverse attributes. The film roughnesses and average spatial wavelengths added to the substrates depend on the multilayer film fabrication conditions, i.e., material combinations, number of layers, and individual layer thickness. These were estimated to lead to a loss of specular reflectivity and variations of the soft x-ray scattering angle distribution. This method points the way to further studies of soft x-ray multilayer film functional properties and can be used as basic guidance for selecting the best coating conditions in the fabrications of soft x-ray multilayer films. (C) 1996 American Vacuum Society.

Beyond simple imaging with energetic beams – nanopatterning, correlative microscopy and statistical analysis of inclusions

Electron microscopy (EM) has advanced in an exponential way since the first transmission electron microscope (TEM) was built in the 1930’s. The urge to ‘see’ things is an essential part of human nature (talk of ‘seeing is believing’) and apart from scanning tunnel microscopes which give information about the surface, EM is the only imaging technology capable of really visualising atomic structures in depth down to single atoms. With the development of nanotechnology the demand to image and analyse small things has become even greater and electron microscopes have found their way from highly delicate and sophisticated research grade instruments to key-turn and even bench-top instruments for everyday use in every materials research lab on the planet. The semiconductor industry is as dependent on the use of EM as life sciences and pharmaceutical industry. With this generalisation of use for imaging, the need to deploy advanced uses of EM has become more and more apparent. The combination of several coinciding beams (electron, ion and even light) to create DualBeam or TripleBeam instruments for instance enhances the usefulness from pure imaging to manipulating on the nanoscale. And when it comes to the analytic power of EM with the many ways the highly energetic electrons and ions interact with the matter in the specimen there is a plethora of niches which evolved during the last two decades, specialising in every kind of analysis that can be thought of and combined with EM. In the course of this study the emphasis was placed on the application of these advanced analytical EM techniques in the context of multiscale and multimodal microscopy – multiscale meaning across length scales from micrometres or larger to nanometres, multimodal meaning numerous techniques applied to the same sample volume in a correlative manner. In order to demonstrate the breadth and potential of the multiscale and multimodal concept an integration of it was attempted in two areas: I) Biocompatible materials using polycrystalline stainless steel and II) Semiconductors using thin multiferroic films. I) The motivation to use stainless steel (316L medical grade) comes from the potential modulation of endothelial cell growth which can have a big impact on the improvement of cardio-vascular stents – which are mainly made of 316L – through nano-texturing of the stent surface by focused ion beam (FIB) lithography. Patterning with FIB has never been reported before in connection with stents and cell growth and in order to gain a better understanding of the beam-substrate interaction during patterning a correlative microscopy approach was used to illuminate the patterning process from many possible angles. Electron backscattering diffraction (EBSD) was used to analyse the crystallographic structure, FIB was used for the patterning and simultaneously visualising the crystal structure as part of the monitoring process, scanning electron microscopy (SEM) and atomic force microscopy (AFM) were employed to analyse the topography and the final step being 3D visualisation through serial FIB/SEM sectioning. II) The motivation for the use of thin multiferroic films stems from the ever-growing demand for increased data storage at lesser and lesser energy consumption. The Aurivillius phase material used in this study has a high potential in this area. Yet it is necessary to show clearly that the film is really multiferroic and no second phase inclusions are present even at very low concentrations – ~0.1vol% could already be problematic. Thus, in this study a technique was developed to analyse ultra-low density inclusions in thin multiferroic films down to concentrations of 0.01%. The goal achieved was a complete structural and compositional analysis of the films which required identification of second phase inclusions (through elemental analysis EDX(Energy Dispersive X-ray)), localise them (employing 72 hour EDX mapping in the SEM), isolate them for the TEM (using FIB) and give an upper confidence limit of 99.5% to the influence of the inclusions on the magnetic behaviour of the main phase (statistical analysis).

Risk mitigation framework for a robust design process

The increasing complexity of new manufacturing processes and the continuously growing range of fabrication options mean that critical decisions about the insertion of new technologies must be made as early as possible in the design process. Mitigating the technology risks under limited knowledge is a key factor and major requirement to secure a successful development of the new technologies. In order to address this challenge, a risk mitigation methodology that incorporates both qualitative and quantitative analysis is required. This paper outlines the methodology being developed under a major UK grand challenge project - 3D-Mintegration. The main focus is on identifying the risks through identification of the product key characteristics using a product breakdown approach. The assessment of the identified risks uses quantification and prioritisation techniques to evaluate and rank the risks. Traditional statistical process control based on process capability and six sigma concepts are applied to measure the process capability as a result of the risks that have been identified. This paper also details a numerical approach that can be used to undertake risk analysis. This methodology is based on computational framework where modelling and statistical techniques are integrated. Also, an example of modeling and simulation technique is given using focused ion beam which is among the investigated in the project manufacturing processes.

Uncertainty analysis to minimise risk in designing micro-electronics manufacturing processes

A design methodology based on numerical modelling, integrated with optimisation techniques and statistical methods, to aid the process control of micro and nano-electronics based manufacturing processes is presented in this paper. The design methodology is demonstrated for a micro-machining process called Focused Ion Beam (FIB). This process has been modelled to help understand how a pre-defined geometry of micro- and nano- structures can be achieved using this technology. The process performance is characterised on the basis of developed Reduced Order Models (ROM) and are generated using results from a mathematical model of the Focused Ion Beam and Design of Experiment (DoE) methods. Two ion beam sources, Argon and Gallium ions, have been used to compare and quantify the process variable uncertainties that can be observed during the milling process. The evaluations of the process performance takes into account the uncertainties and variations of the process variables and are used to identify their impact on the reliability and quality of the fabricated structure. An optimisation based design task is to identify the optimal process conditions, by varying the process variables, so that certain quality objectives and requirements are achieved and imposed constraints are satisfied. The software tools used and developed to demonstrate the design methodology are also presented.

Optimisation methodology for risk mitigation in advanced micro-system electronics manufacturing

This paper presents a design methodology based on numerical modelling, integrated with optimisation techniques and statistical methods, to aid the development of new advanced technologies in the area of micro and nano systems. The design methodology is demonstrated for a micro-machining process called Focused Ion Beam (FIB). This process has been modelled to provide knowledge of how a pre-defined geometry can be achieved through this direct milling. The geometry characterisation is obtained using a Reduced Order Models (ROM), generated from the results of a mathematical model of the Focused Ion Beam, and Design of Experiment (DoE) methods. In this work, the focus is on the design flow methodology which includes an approach on how to include process parameter uncertainties into the process optimisation modelling framework. A discussion on the impact of the process parameters, and their variations, on the quality and performance of the fabricated structure is also presented. The design task is to identify the optimal process conditions, by altering the process parameters, so that certain reliability and confidence of the application is achieved and the imposed constraints are satisfied. The software tools used and developed to demonstrate the design methodology are also presented.

Scaling of domain periodicity with thickness measured in BaTiO3 single crystal lamellae and comparison with other ferroics

The focused ion beam microscope has been used to cut parallel-sided {100}-oriented thin lamellae of single crystal barium titanate with controlled thicknesses, ranging from 530 nm to 70 nm. Scanning transmission electron microscopy has been used to examine domain configurations. In all cases, stripe domains were observed with {011}-type domain walls in perovskite unit-cell axes, suggesting 90 degrees domains with polarization in the plane of the lamellae. The domain widths were found to vary as the square root of the lamellar thickness, consistent with Kittel's law, and its later development by Mitsui and Furuichi and by Roytburd. An investigation into the manner in which domain period adapts to thickness gradient was undertaken on both wedge-shaped lamellae and lamellae with discrete terraces. It was found that when the thickness gradient was perpendicular to the domain walls, a continuous change in domain periodicity occurred, but if the thickness gradient was parallel to the domain walls, periodicity changes were accommodated through discrete domain bifurcation. Data were then compared with other work in literature, on both ferroelectric and ferromagnetic systems, from which conclusions on the widespread applicability of Kittel's law in ferroics were made.

Three-dimensional macroporous silicon photonic crystal with large photonic band gap

Three-dimensional photonic crystals based on macroporous silicon are fabricated by photoelectrochemical etching and subsequent focused-ion-beam drilling. Reflection measurements show a high reflection in the range of the stopgap and indicate the spectral position of the complete photonic band gap. The onset of diffraction which might influence the measurement is discussed.

Impulsive electric fields driven by high-intensity interactions

The interaction of high-intensity laser pulses with matter releases instantaneously ultra-large currents of highly energetic electrons, leading to the generation of highly-transient, large-amplitude electric and magnetic fields. We report results of recent experiments in which such charge dynamics have been studied by using proton probing techniques able to provide maps of the electrostatic fields with high spatial and temporal resolution. The dynamics of ponderomotive channeling in underdense plasmas have been studied in this way, as also the processes of Debye sheath formation and MeV ion front expansion at the rear of laser-irradiated thin metallic foils. Laser-driven impulsive fields at the surface of solid targets can be applied for energy-selective ion beam focusing.

Excited ions in intense femtosecond laser pulses: Laser-induced recombination

Electron-ion recombination in a laser-induced electron recollision is of fundamental importance as the underlying mechanism responsible for the generation of high harmonic radiation, and hence for the production of attosecond pulse trains in the extreme ultraviolet and soft X-ray spectral regions. By using an ion beam target, remotely prepared to be partially in long-lived excited states, the recombination process has for the first time been directly observed and studied.

Electron and laser interactions with positive ions

Recent progress in laboratory-based electron-ion scattering is reviewed, and the sensitivity of observed interference structure as a probe of collision dynamics is discussed. The extension of our use of positive ions as scattering targets to photon-ion interactions is demonstrated with the first ion-beam measurements for the fragmentation of a molecular ion, H-2(+), using intense femtosecond laser pulses.

Nanoscale ferroelectrics machined from single crystals

This paper summarises some of the most recent work that has been done on nanoscale ferroelectrics as a result of a joint collaborative research effort involving groups in Queen's University Belfast, the University of Cambridge and the University of St. Andrews. Attempts have been made to observe fundamental effects of reduced size, and increasing morphological complexity, on ferroelectric behaviour by studying the functional response and domain characteristics in nanoscale single crystal material, whose size and morphology have been defined by Focused Ion Beam (FIB) patterning. This approach to nanoshape fabrication has allowed the following broad statements to be made: (i) in single crystal BaTiO3 sheets, permittivity and phase transition behaviour is not altered from that of bulk material down to a thickness of similar to 75 nm; (ii) in single crystal BaTiO3 sheets and nanowires changes in observed domain morphologies are consistent with large scale continuum modeling.